ANATOMY

Detailed explanation-1: -IgM is the primary antibody produced during an initial antigen challenge. Yet, upon subsequent antigen exposure, follicular B cells undergo isotype switching, resulting in IgG, IgG, IgE, or IgA production.

Detailed explanation-2: -The first antibody produced is manily IgM (although small amounts of IgG are usually also produced).

Detailed explanation-3: -IgM is the first antibody isotype produced during an immune response and functions as a primary barrier against pathogens. IgM also regulates immune responses. Thus, antigen-specific IgM administered before immunization enhances antibody response, which depends on complement (1).

Detailed explanation-4: -The third option is IgG. It is the most abundant antibody in primary and secondary response, it crosses the placenta, and provides passive immunity to the foetus. The fourth option is IgM. It is the first class of antibodies which is released by B cells during primary response.

Detailed explanation-5: -The secondary antibody response is characterized in its first few days by the production of small amounts of IgM antibody and larger amounts of IgG antibody, with some IgA and IgE.